I can help you with short definitions:
Apache: all purpose open source web server written in C
Tomcat: open source web server written in
Java. Mostly used for small projects.
Websphere: This is the application server from IBM for large projects, like banking applications
JBoss: Open source application server
Basically a web server is meant for the web and an application server for ehm applications. Tomcat can be used as standalone web server, but if you want better security
you should link it with Apache.